When drilling in earth formations, the control (i.e., processing and handling) of solid materials (such as “cuttings”-pieces of a formation dislodged by the cutting action of teeth on a drill bit) is of great importance. A variety of machines, such as shakers, centrifuges, blowers, pumps (including mud pumps), agitators, mixers, draw works, conveyors, etc. are used in the processing and handling of solid materials created during the drilling or completion stage. Combinations of these machines may also be used and such machines are well known in the art.
A typical concern, for example, is how to handle cuttings from the formation being drilled. After the cuttings have been transported to the surface of the well by a flow of a drilling fluid, disposal of the cuttings may pose a problem, particularly when the drilling fluid is oil-based or hydrocarbon-based. The oil from the drilling fluid (as well as any oil from the formation) often becomes associated with or adsorbed to the surfaces of the cuttings. The cuttings are then an environmentally hazardous material, making disposal a problem especially in environmentally sensitive areas such as offshore operations.
U.S. Pat. No. 5,857,955 discloses one prior art centrifuge for use in oilfield applications. In particular, a centrifuge may be used to aid in the removal of dirt, sand, shale, abrasive cuttings, and/or silt particles from drilling fluid after the fluid has been circulated through a well so as to lift cuttings and other debris to the surface in an oilfield drilling operation. Moreover, U.S. Pat. No. 6,283,303 discloses a vibrating screen separator including an elongated, box-like, rigid bed, and a screen attached to, and extending across, the bed. The bed vibrates as the material to be separated is introduced to the screen, and the screen retains relatively large size material and passes the liquid and/or relatively small material into the bed. The bed can be vibrated by pneumatic, hydraulic, or rotary vibrators, and other means known in the art.
Operational control of the power transmission and forces (such as torque, conveyor speed, pump rate, etc.) involved with the types of oilfield devices such as those listed above is important to ensure efficient operation and to avoid failure of, for example, couplings and the like. Adjusting the rotational speed of (and the torque applied to) the drive shaft allows a user to maintain predetermined optimum operating conditions, regardless of variances in the flow rate of the feed slurry. Such techniques using variable speed AC motors are known in the art. However, such variable speed motors may be quite expensive. In particular, U.S. Pat. No. 5,857,955 (assigned to the assignee of the present invention and incorporated by reference herein) discloses one prior art variable speed AC motor. It is expressly within the scope of the present invention that other rare earth, permanent magnets may be used other than those described herein.
Therefore, what is needed are devices and methods that improve the reliability, safety, and/or energy efficiency of oilfield machinery.